The story actually doesn't tell us much about how Fezziwig feels about Scrooge, specifically.
Instead, we are shown how Fezziwig treats all of his employees and we see how Scrooge feels about Fezziwig.
First, Fezziwig treats all of his employees almost as an extension of his own family. By throwing a large Christmas celebration for his employees, even those in the lowest positions (like Scrooge was at the time), he is demonstrating that everyone in his business has value and that he wants them to know how much he appreciates them. He is warm, caring, and generous to his employees, including Scrooge.
Scrooge remembers Fezziwig very fondly and looks back on his time at Fezziwig's with happiness. It is obvious he learned a lot about the business of money lending from his former employer and went on to prosper. Sadly, he did not learn some of the social skills and kindness that Fezziwig so clearly taught him as well.